As is well known, X-rays are attenuated according to an X-ray attenuation coefficient, such as photoelectric effect, Compton scattering, and the like, of a substance placed in a path of the X-rays.
X-ray radiography is a radiography method using straightness and attenuation of X-rays, and based on the amount of attenuation accumulated in the course of the X-rays passing through a field of view, it provides an X-ray image of the internal structure of the field of view. To achieve this, an X-ray imaging system includes: an X-ray generation apparatus configured to irradiate X-rays to a field of view; an X-ray sensor disposed to face the X-ray generation apparatus with the field of view therebetween, and configured to detect X-rays that have penetrated through the field of view; and an image processing apparatus configured to construct a gray-level X-ray image of an internal structure of the field of view by using X-ray projection data, as a detection result detected by the X-ray sensor.
Meanwhile, in recent years, X-ray radiography has been rapidly evolving into DR (Digital Radiography) using digital sensors due to the development of semiconductor and information processing technologies, whereby image processing technology has also been developed and is used in various ways according to the purpose and application field.
As an example, FIG. 1 is a view showing principle of intra-oral X-ray radiography mainly used in the dental field, and an intra-oral X-ray image according to the intra-oral X-ray radiography.
As shown in the drawing, intra-oral X-ray radiography is an X-ray radiography technology for obtaining an X-ray image of a limited field of view of a subject, and is performed as follows: an X-ray sensor S is placed inside the subject's mouth; and X-rays are irradiated from an X-ray generation apparatus outside the mouth to the X-ray sensor S, thereby obtaining an X-ray image of a tooth and surrounding tissue that is disposed between the X-ray generation apparatus and the X-ray sensor S. The intra-oral X-ray image has advantages of low distortion, excellent resolution and sharpness, and relatively low radiation exposure, so it is mainly used for implant treatment or endodontic treatment requiring high resolution.
However, the conventional intra-oral X-ray image is a two-dimensional transmission image, in which results of X-ray attenuation by all the substances including a tooth and surrounding tissue, namely a field of view, that exist between the X-ray generation apparatus and the X-ray sensor S are superimposed on a two-dimensional plane defined as the incident surface of the X-ray sensor S. Thus, with the intra-oral X-ray image alone, it is impossible to identify a depth of a desired portion, such as s focus, within the area of the X-ray image, that is, relative positional relationship of the path of the X-rays.
Accordingly, for more accurate diagnosis, such as a three-dimensional location of a desired portion of the intra-oral X-ray image, CT scans are additionally performed to obtain a three-dimensional X-ray image of the field of view or diagnosis is made based entirely on the empirical knowledge of the radiologist. However, in the former case, the overall length of time and procedures are complicated and subject fatigue is increased, as well as a serious problem of unnecessarily increasing radiation exposure, and in the latter case, there is a deviation of diagnostic results according to the personal experience of the radiologist, and there is a high possibility of subjective judgment, which lowers the reliability of diagnosis.